Single station range finder with variable base



Sept. 5, 1939. 0.. EPPENSTEIN SINGLE 5mm rumor: FINDER wmi mum: ms:

Filed March 8, 1938 A Imam-z Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE SINGLE STATION RANGE FINDER WITH VARIABLE BASE Otto Eppenstein, Jena, Germany, assignor to the firm of Carl Zeiss, Jena, Germany Application March 8, 1938, Serial No. 194,64 In Germany March 23,1937

4 Claims.

1 wherein e-is the range to be measured, 17 the base, and 6 the parallactic angle at the target. The device which is used in said rangeflnders for changing the base b is generally provided with means indicating direct the ranges e correspond- 15; mg to different bases 1). The actual distance of an object coincides with the indicated one, however, only when deviations a falsifying the parallactic angle 6 do not arise in the rangefinder itself, or when these errors a, which are hereinafter, mstermed adjustment errors, have been compensated in any suitable manner. In rangeflnders producing a variable parallactic angle at the target, these adjustment errors are eliminated, as

is well known, by means or a double measurement as; eflected through the agency of two different bases of definite lengths.

The invention makes use of a method 01 compensating the adjustment errors in single station rangeflnders with variable base, this method consisting in the range measurement being affected with a definite parallactic angle at the target and repeated with another parallactic angle, the actual range being proportional to the difierence in the base lengths inthe two measurements. Ac-

;cordingly, two measurements are' effected subsequently to each other, the first with a definite parallactic angle 6 depending on the construction of the apparatus, and the second with a definite para lactic angle k.6, in which it can have, on principle, any magnitude differing from The invention is based on the following consideration: If v be the telescopic magnification of a rangefinder having a variable base I), the

parallax A seen in the field of view of this rangefinder is in the case of a target at a distance e In rangefinding, the base 27 is known to be varied until the parallax A has assumed the magnitude 0. Accordingly,

55 Apart from the practically unavailable case in which the base b as well as the parallactic angle a and the adjustment error 8' assume the mag-- nitudes 0 at one and the same 3 is arrived at when time, the Equation This equation corresponds to the Equation 1 when an adjustment error has been taken into consideration. Evaluating the measurement 'by means of Equation 4 will yield an incorrect range when the division pointed at by the indicating device represents, as usual, ranges based on Equation '1.

- Substituting an angle 10.6 for the parallactic angle 6 entails a compensation of the parallax 'A as soon as the base b is changed to 12, which depends on the equation The elimination of the angle 6' in the Equations 4 and 5 provides for the range e an Equation 6, which is withoutthe adjustment error 8':

b b (6) a 1-k When accordin ly, a target at a range e is measured once with the parallactic angle 8 and once with the parallactic angle 70.6, the actual range e is proportional to the difference of the two determined bases b and b" and not influenced by any adjustment error 6", which can be assumed tobe the same in both the said measurements. Eifecting this double measurement depends on the possibility of varying the definite parallactic angle 6 to kit. This change-can be eiiected, for instance, by means of an additional retracting prism producing in one of the ray paths a deviation 8 (l-k) or by substituting a prism of the deviation ks for the prism of the deviation 8. Especiallysimple proceedings are arrived at by using the factor k=1 or k=il. In the case of the factor k=l, which can be realized by rotating in one of the ray paths a prism of the deflection 6 about the optical axis through 180, the numerical values of the parallactic angles at the target are the same in 'both measurements. 'In the case of the factor k=0, the parallactic angle is zero in the second measurement, this system which can be made to assume two such positions in one of the imaging ray paths as to I produce two inversely equal deviations of the imaging ray pencils in the measuring plane. It is advisable in the 'case of the said other method to provide that the optical deviating system which is so disposed in one of the two imaging ray paths as to deflect the imaging ray pencil in the measuring plane has dimensions permitting it to influence at the same time both the said pencils when the base of the rangeflnder assumes approximately the magnitude zero. This can be arrived at in a simple manner in a rangefinder having a monocular telescope and whose ray entrance apertures correspond to the upper and the lower half of the telescope objective, when each of the two systems deviating at 90 (for instance pentagon prisms), which are,

as a rule, always in the ends of the base, is only half as high as the telescope objective, and when both systems are placed in the'second measurement above each other on the eye-piece side of the system of the deviation 6 lying in one of the ray paths and being, in its turn, so dimensioned as to correspond to the entire height of theo vtelescope objective. An instrument thus constructed acts in the second measurement as a rangefinder which has a variable base and whose definite parallactic angle at the target corresponds to the adjustment error 6. As this error is always comparatively insignificant, the second measurement requires such a change of the base b from b=0 as is so slight that the rays entering the deviating systems in the base ends are deviated substantially at an angle 6 when traversing the unchanged system.

,In a telescope in whidh the imaging rays can enter only through the one half of the objective, the produced image is known to cover neverthelessjthe entire image field. In a rangefinder of the construction described last, the two imaging ray pencils would, accordingly, produce over-v lapping images which, per se, would allow the.

measurement of ranges by variation of the base I) until these overlapping images cover each other completely. Exact adjustments being, however, very difficult in this" case, it is preferable not to use overlapping images. Moreover, each of the two imaging ray paths requires an exit pupil of I its own, which may give rise to measuring errors.

The telescopic system of the rangefinder is suitably provided with a bi-prism the ridge of which is parallel to the measuring plane and lies in the image plane of the telescope, and whose base surface is parallel to the imaging plane and which has such angles of refraction that the exit pupils of the upper and the lower half of the objective overlap each other in part, the plane of these exit pupils containing a diaphragm whose diaphragm aperture corresponds to thoseparts of the exit pupils which these pupils have in commen, and the remaining part of said pupils being rendered inefiective by the diaphragm. It -is thus attained that there are visible in the field of view of the telescope two partial images of the target, which areseparated by a sharp line,

viz the ridge of the bi-prism, and whose coincidence is effected in the measurement.

In the accompanying drawing, which illustrates two constructional examples of the invention, Figure 1 shows the one example in plan view, Figure 2 is a section through line AA pentagon prism II).

in Figure 1, and Figure 3 represents the other example in" a view ofiered to the eye when looking at the apparatus from the target. Both examples concern monocular rangeflnders with variable base. I

The rangefinder according to the first example (Figures 1 and 2) has a monocular telescope I, whose optical parts are an objective 2, a collective lens 3 and an eye-lens 4. In the eye-piece 3, 4- of the telescope I, a diaphragm 5 is disposed in such a manner that the diaphragm aperture 6 lies approximately in the plane of the exit pupil. A prism housing I and a guiding rule 8 are rigidly connected to the telescope I. The housing I contains a triangle prism 9,which is so disposed in the ray path and of such height as to cover the objective 2 entirely, and a pentagon prism III, which is only half as high as the prism 9 and coordinated to the upper half of the objective 2. A cuneiform prism I2 in a mount II on the prism housing I is disposed near the object side of the pentagon prism III in such a. manner that its edge of refraction intersects the principal plane of the prism I0 at right angles. The height of the cuneiform prism I2 corresponds to the vertical diameter of the objective 2. The guiding rule 8, which is disposed on the lower part of the prism housing 1 and projects to-the right of the observer at the telescope I, is parallel to the measuring plane determined by the principal planes of the prisms 9 and III and provided with a scale I3 representing ranges. A slide I4 displaceable on the rule 8 is provided with a window I6 having an index I! and carries a pentagon prism I5 corresponding to the In the telescope I, a biprism I8 is so disposed that its ridge I9 liesin, and its base surface is parallel to, the image plane of the telescope I.

the measuring plane.

The zero line of the scale I3 coincides with the index I] when the slide Il assumes that position on the rule 8 in which the contours oi the pentagon prisms Ill and I5 cover each other.

' The space between the division lines of the scale I3 are determined according to the Equation 6,

the magnitude 1c being assumed to be zero. As each of the prisms I0 and 9 deviates the entering imaging pencils at the deviation of the rays by the cuneiform prism I2 corresponds to the predetermined parallactic angle at the target.

, To the upper and the lower half of the objecthese exit pupils out of the sight of the observer at the eye-piece, and there appears in the field of view a sharp horizontal line, viz. the ridge I9 of the prism I8, which separates the images produced by the two halves of the objective.

The ridge I9 is parallel to When in use, the apparatus is so directed to the target whose distance is to be measured that the observer looking into the eye-lens 4 secs two images of the target lying above each other. By.

displacing the slide I4 on the rule 8 to the right, these images are made to coincide, and the range magnitude corresponding to this coincidence and indicated by the index I1 is read on the scale I3. The slide 14 is then displaced to the left until the prism I5 lies belo'w'the prism I0 and in the rear of the prism I2, whereupon the prism I2 deviates the imaging ray pencils entering the prisms l and IS. The images produced in the telescope I would coincide when the index I! is in coincidence with the zero line of the scale I3 if the apparatus were devoid of adjustment errors. Exact coincidence is obtained, however, by another displacement of the slide II, this other displacement being comparatively insignificant in most cases. Also the range magnitudes corresponding to this other measurement is to be read on the scale lit. The actual range of thetarget corresponds to the diflerence of the said two magnitudes indicated on the scale l3. If. for instance, the first reading is 169 metres and the second 3 metres, the real range, 1. e., the magnitude of the range without adjustment errors, is 172 metres.

The second constructional example (Figure 3) difiers from the first example in that its prisms 9 and I 0 are disposed in separate housings 26 and 2|, respectively. The housing 2! is a slide displaceable on another rule 22 fast with the housing 2Q. The cuneiform prism I2 is in a rotatable mount 23 whose rotation is restricted to 180 by a pin 24 fast with this mount and two stops 25 fast with the housing 2| In the two extreme positions of the mount 23, the refraction edge of the prism I2 is at right angles to the measuring plane. The rule I has a scale 26 on which an index 21 on the slide l4 indicates ranges. The rule 22 has a scale 26 indicati ranges which corresponds to the scale 26, the zero lines of these two scales being in coincidence. To the scale 26 belongs an index 29 on the prism housing 2 I. The two constructional examples are the same in all other respects.

The range of a target is determined without any adjustment errors by means of two measurements also with the apparatus according to the second example. When the pin 24 touches one of the stops 25 and the index 29 is adjusted to the zero line of the scale 28, the slide II is displaced until the two target images are seen in coincidence in the eye-piece. Subsequently to the magnitude corresponding to this coincidence position having been read on the scale 26, the slide I4 is to be displaced to the left until the index 21. coincides with the zero line of the scale 26. The prism housing 2| is then.displaced to the right, and the mount 23 containing the cuneiform prism I2 is rotated until the pin- 24 touches the other stop 25. Byfurther displacement of the prism housing 2| on the rule 22, the two target images visible in the fleld of view of the telescope I are made to coincide again,

and the corresponding magnitude, indicated by the index 29, is read on the scale 26. The exact range, 1. e., the range without errors, is obtained according to Equation 6, which reads in this case b1 and be being the two base lengths determined.

As the change in the positions of the prisms Ill and IS in the two measurements entails reverse directions of the determined base lengths, the

second base length is to besubstituted negatively for k= 1, the difference of the bases being, accordingly, the sum of the absolute lengths.

The lines of the scales 26 and 26 are naturally so spaced as a rule that the determination of the range can be effected simply by adding the two read magnitudes.

I claim:

1. A rangeflnder comprising a housing, a telereflecting system consisting of two reflecting members displaceable relatively to each other, each of the ray entrance apertures of said members corresponding to one half of the ray entrance aperture of said telescope system, at least one slide, said slide being displaceable relatively to said housing, one of said reflecting members being mounted on said slide, means indicative of the distance apart of said members, and a cuneiform deviating prism for deviating the imaging rays at a-deflnite angle, said deviating prism being in front of the ray entrance aperture of one of said reflecting members, and the ray entrance aperture of said deviating prism corresponding to the .entire ray entrance aperture of said telescope system.

2. In a rangeflnder according to claim 1, one of said reflecting members being rigidly connected to said housing, said cuneiform deviating prism being connected to last said reflecting member, a rule flxed to said housing, said slide being displaceably mounted on said rule, and said means indicative of the distances apart of said reflecting members being a scale on said rule and an index on said slide.

3. In a rangeflnder according to claim 1, a reflecting system for deviating the imaging ray pencil of said telescope system at right angles, a bi-prism for doubling the exit pupil of said telescope system, the last said reflecting system and said bi-prism being disposed in said housing. the ridge of said bi-prism being parallel to the direction of relative displacement of said reflecting members and lying in the image plane of said telescope system, and a diaphragm, the aperture of said diaphragm being approximately in the plane of the exit pupil of said telescope system and corresponding to that portion of this plane in which parts of the doubled exit pupil overlap each other.

4. A rangeflnder comprising a housing, a telescope system containing an objective and an eyepiece being disposed in said housing, a reflecting system for deflecting the rays of two imaging ray pencils at 90 into said telescope system, said reflecting system consisting of-two reflecting members displaceable relatively to each other, each of the ray entrance apertures of said members corresponding to one half of the ray entrance aperture of said telescope system, two slides, two rules parallel to each other and disposed on said housing, one of said slides being displaceably mounted on the one of said rules, said other slide being displaceably mounted on the other of said rules, each of said reflecting member being fixed to one of said slides, means indicative of the distance apart of said reflecting members consisting of a scale representing ranges disposed on each of said rules and an index disposed on each of said slides, a cuneiform deviating prism for deviating the imaging rays at a definite angle, said cuneiform prism being 'rotatably mounted in front of the ray entrance aperture of one of said reflecting members on one of said slides. the ray entrance aperture of said cuneiform deviating prism corresponding to the entire ray entrance aperture of said telescope system, and

means for restricting the rotation of said cuneiform prismto 180.

O'I'IO EPPENSTEIN. 

